The present invention relates to a special section of well casing that is particularly useful in offshore wells that have under-compacted formations. As hydrocarbon production has moved into deeper waters off-shore, the producing formations have often been younger, under-compacted reservoirs. As these reservoirs are produced, they compact which results in axial loading and casing deformation. In many cases, the deformation of the casing has been extensive enough to cause loss of the producing wells. Since offshore production is typically from a structure having limited space, the loss of a well can seriously affect the total production from the structure. Well replacement is typically difficult, if at all possible, and always results in significant additional expense. When conditions preclude well replacement, the hydrocarbon reserves are lost forever.
One obvious solution to the problem of casing damage caused by axial load due to formation compaction would be to provide some sort of slip joint in the casing that would allow the casing to shorten without damage such as buckling or collapsing. While the slip joint would solve the problem of buckled or collapsed casing, it requires seals or other means for isolating the formation from the interior of the casing.
In addition, if slip joints are used as part of a well casing, some means must be provided for preventing the slip joint from collapsing as the casing is installed in the well. In addition to preventing the slip joint from collapsing, structure must be included for preventing it from extending beyond its limits as the casing is hung free in the well. Both of these requirements involve complicated mechanical arrangements that are, of course, subject to failure in a well. Obviously, if the slip joint compresses during installation of the casing, it will not provide protection against casing collapse when the reservoir compacts.